Telomeres protect chromosome ends, and telomerase synthesizes and replenishes the telomeric DNA central to the protective DNA-protein complex of the telomere. Budding yeast will be used to investigate essential and conserved processes of telomere maintenance. Aim 1 focuses on interactions of core telomeric protein components (yeast Rap1 and Rif2) with telomeric DNA, to dissect fundamental mechanisms underlying the dynamics of their associations, which are crucial to telomere function. It was found that telomere/telomerase status is constantly monitored in cells, with loss of telomere maintenance in yeast causing responses at a stage earlier than previously thought. The details of the interactions that affect yeast cell proliferation upon such early telomerase loss will be dissected: Aim 2 will identify the immediate molecular lesion at telomeres caused by telomerase inactivation, and examine immediate cellular responses to telomerase shut-off. Two growth-controlling pathways were identified that cross-talk with telomere maintenance status: in combination with early telomerase loss, disruption of either DNA damage checkpoint signaling or TOR signaling causes lethality. Aim 2B will test models for the requirement of DNA checkpoint proteins Mrc1 and Rad9. Aim 3 will test models for how TOR signaling pathways and early telomere loss interact. Pursuing the finding that early telomerase loss causes major defects in meiosis, Aim 4 wil test the molecular requirements for telomerase and telomeres for successful meiosis. Finally, given the intersection of telomere status with TOR signaling, which affects cell aging, and other recent evidence, Aim 5 will examine the role of telomere deprotection in the budding aging of yeast mother cells. Understanding the mechanisms by which telomere maintenance status is sensed and integrated with pathways that control cell proliferation is a core goal of this proposal. This project is thus highly relevant to how telomere status integrates with other cellular processes, such as nutritional signaling, that regulate human aging, morbidity and mortality.